Flattening the bird halves the cooking time and doubles the crisp skin. Weight on top is what makes the difference.
Kitchen shears, cutting up either side of the backbone from tail to neck. It takes about a minute and the bones cut easily — you are going through rib joints, not through the spine itself.
Keep the backbone. It goes into the stock pot with everything else. Full jointing guide →
Turn the bird breast up and press down hard on the breastbone with the heel of your hand until you feel it give. It will crack, and that is correct. The bird should now lie completely flat, which is the entire point — every part of it is now the same distance from the heat.
Salt both sides. On a rack, uncovered, four hours minimum and overnight if you have the time. Flat birds dry faster than whole ones, so even a short spell in the fridge makes a visible difference to the skin.
Oven to 220 °C. Heavy oven-proof pan on the hob over a medium-high flame with the oil. Wait until the oil moves like water and just starts to shimmer.
Bird into the pan skin down. Put the second pan on top and press. Six to eight minutes without moving it — you are listening for a steady sizzle rather than a roar, and looking for the edges to go deep brown.
Pan and all, weight still on top, twenty-five to thirty minutes. The skin side stays down the whole time.
Check the thigh for 72 °C. A flattened bird cooks in roughly half the time of a whole one at the same weight, which is the other reason to do this.
Ten minutes on a board. Cut into eight or into rough pieces, squeeze the lemon over, scatter the thyme.
Pour the fat from the pan over the pieces. It has lemon and thyme in it and it is the best part.
It was moved too early. Protein sticks to hot metal on contact and then releases on its own once a crust has formed underneath — usually four or five minutes in. If you try to lift or shift the bird before that, the skin tears and stays behind.
Leave it alone. When it is ready it will slide when you nudge the pan, and until then it will not.